The present invention relates generally to wireless communications systems and more particularly to a method for implementing power control at the forward link of a cellular code division multiple access (CDMA) network.
A code division multiple access (CDMA) cellular network consists of base stations geographically distributed throughout a service area, and mobile stations. Each base station provides digital telephony service to mobile stations located in the station""s designated geographical region. Wireless communications between a mobile station and a base station in a CDMA network organized in accordance with the IS-95 standard from the Telecommunications Industry Association occur on both reverse and forward CDMA channels. The reverse CDMA channel carries traffic and signaling information from the mobile station to the base station. The forward CDMA channel carries traffic and overhead information including pilot, synchronization and paging, from the base station to the mobile station.
Numerous parameters, including mobile velocity, multipath fading and handoff conditions factor into calculating service quality, which is defined by frame error rate (xe2x80x9cFERxe2x80x9d), for a CDMA network. IS-95A, an Electronic Industries Association standard similar to IS-95, specifies a message-based forward power control protocol for the first-rate set, employing a feedback loop, to report service quality from a mobile station to a base station. In this protocol, the mobile station reports the FER to the base station via a series of periodic blank and burst messages, sent either upon the occurrence of a pre-specified time interval, or when the FER exceeds a predetermined threshold. Upon receipt of an FER report the mobile station must decode the message, thereby realizing a delay, before acting upon it. The delay realized during this processing decreases the accuracy of the reported FER. The combination of periodic reporting and decoding delay prohibit a first-rate set IS-95A-based system from closely tracking service quality.
Closely tracking service quality is integral to achieving system efficiency. An algorithm that closely tracks service quality permits operation at lower average transmit power than one that tracks poorly because the tracking process allows a system to determine the amount of power needed by each frame, thereby avoiding both waste and over-allocation of transmission power. Consequently, allocation of transmission power to users is equalized and a system may achieve efficiency. Efficient systems operate at higher capacity than do inefficient systems. Thus, a net capacity gain results from close tracking of service quality.
Systems and methods consistent with the present invention address the problem of lost system capacity, allowing a system to operate efficiently, through close tracking of service quality on the forward link of a cellular CDMA system. By applying the optimal amount of power to each frame, a system consistent with the principles of the present invention avoids waste and over-allocation of power to any frame. After determining the optimal transmission power level for a given frame relative to the amount of noise and interference on the cellular link, the current power level is adjusted to reflect the optimal level.